Field of the Invention
The invention pertains to single-channel and multi-channel optical connections. Such connections are implemented with optical end pieces for connecting one or more optical fiber ends in a coupling fashion. Within the scope of the present invention, an optical fiber is to be understood as a conductor suitable for guiding and relaying an optical signal, such as, for example, an optical fiber assembly, optical fiber ribbons or optical conductors constructed on a substrate (so-called waveguides).
More particularly, the invention relates to an optical end piece for endwise connection of one or more optical fibers, having a coupling surface at which the optical fiber or fibers terminate.
Such an end piece--described in U.S. Pat. No. 5,214,730 to Nagasawa et al. (EP 0 712 015 A2)--holds several optical fiber ends arranged in parallel in a common plane. The end faces of the optical fibers, which serve the purpose of optical coupling, lie in a common coupling surface of the end piece, which is also denoted as a coupling member or ferrule. It is possible via the end face to launch optical signals of a coupling partner into the respective optical fiber and/or to couple out optical signals guided in the respective optical fiber to a coupling partner. Because of the comparatively small dimensions of the light-conducting core cross sections in optical fibers, optimum alignment of the coupling partners relative to one another is important for low coupling losses, that is to say for a high so-called coupling efficiency. In accordance with U.S. Pat. No. 5,214,730, it is desirable to have an aligned, direct body contact of the optical fiber end faces on the side of the coupling partners, particularly in the case of optical coupling of two similar end pieces each having several optical fiber ends. Proposed for this purpose are, inter alia, specially shaped (e.g. cambered, domed) coupling surfaces and the application of adequate axial compressive forces.
However, this still leaves unsolved the problem, which occurs with end pieces both for a single optical fiber end and for several optical fiber ends (also denoted as multiple connectors or MT ferrules), of constructing the coupling surface exactly at right angles to the optical fiber ends and the endpiece geometry in particular of the aligning means or aligning surfaces of the end piece. Whereas in the case of circular cylindrical connectors having only one optical fiber end and thus one punctiform, central coupling contact, it is possible to circumvent this problem by rounded grinding of the connector pin end face (coupling surface), in the case of an elongated coupling surface it is necessary, in particular, to ensure that the coupling surface is situated at a correct angle in the surface desired after processing of the coupling surface, or in the desired plane in the case of plane coupling surfaces. Specifically, if after endside preparation of the end piece the coupling surface is produced `askew`, that is to say not parallel to the desired surface, the coupling efficiency is substantially worsened. In the worst case, optical transmission is even impossible. Thus, for example, in the case of a desired direct contact between the coupling surfaces on the side of the coupling partners, it is possible, in addition to partial contact, for an undesired air gap to be produced in the remaining region between the two coupling surfaces because of a coupling surface, of one of the coupling partners, which has angle faults.